Phase-separated Pr0 Research Articles

Modulation of persistent magnetoresistance by piezo-strain effect in manganite-based heterostructures

Persistent magnetoresistance effects in the phase-separated Pr0.65(Ca0.25Sr0.75)0.35MnO3/SrTiO3 and Pr0.65(Ca0.25Sr0.75)0.35MnO3/0.7PbMg1/3Nb2/3O3–0.3PbTiO3 heterostructures under a low magnetic field are investigated. It is observed that the persistent magnetoresistance effects decrease with increasing temperatures and the values for the heterostructures on 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 and SrTiO3 substrates are about 86.6% and 33.2% at 40 K, respectively. More interestingly, the applied electric field on the 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 substrate can suppress the persistent magnetoresistance effect, indicating that different energy landscapes can be dramatically modulated by the piezo-strain. These results are discussed in terms of the strain-induced competition in the ferromagnetic state and the charge-ordering phase by the energy scenario, which provide a promising approach for designing devices of electric-magnetic memories in all-oxide heterostructures.

Electric-field modulation of photoinduced effect in phase-separated Pr0.65 (Ca0.75Sr0.25)0.35MnO3/PMN-PT heterostructure

In this letter, we report the photoinduced effect modulated by different electric fields in the Pr0.65 (Ca0.75Sr0.25)0.35MnO3/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 heterostructure. The film exhibits a decrease in the resistance up to five orders of magnitude by enhancing applied electric fields, combined with an electric-field-induced insulator-to-metal transition. More interestingly, a reversible bistability arises in the photoinduced change in resistance at T < 80 K as the voltages are increased. The results can be attributed to the phase separation in manganites, which provides a prototype of photoelectric conversion for electric-field modulation of all-oxide heterostructures.

Colossal elastoresistance and strain effects on phase-separated Pr0.5Sr0.5MnO3 films

We have studied the electrically tunable strain effects on phase-separated Pr0.5Sr0.5MnO3 films epitaxially grown on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (001) substrates. Upon cooling, the film shows a ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition at low temperature. Such a transition is depressed and finally disappears in electrical properties with increasing electric field applied on the substrate. Under an electric field of 6 kV/cm, a large reversible resistance drop (∼85%) as well as an enhancement of magnetization is achieved. In situ X-ray diffraction indicates that the substrate-induced strain plays a crucial role in determining the properties in the film by tuning the phase competition between the ferromagnetic metallic and antiferromagnetic insulating state. The FMM-AFI transition in the film is demonstrated to be originated from a large biaxial strain. With decreasing strain, the FMM state is enhanced, leading to a colossal elastoresistance.

Exchange bias and enhanced coercivity in phase separated La0.45Sr0.55MnO3 and Pr0.55(Ca0.65S0.35)0.45MnO3 films

An epitaxial La0.45Sr0.55MnO3 (LSMO) film, which has a paramagnetic-to-ferromagnetic transition at ∼260 K and a partial ferromagnetic-to-antiferromagnetic transition at ∼150 K upon cooling, was synthesized on (001) (La0.18Sr0.82)(Al0.59Ta0.41)O3 with pulsed laser deposition. The x-ray diffraction pattern showed interference fringes around the (002) LSMO peak, indicating a successful growth of a high quality and smooth film. When the LSMO film was cooled down in a magnetic field of 5 kOe, it exhibited a large exchange bias (HEX) of ∼490 Oe and an enhanced coercivity (HC) of ∼800 at 10 K, respectively. The observed exchange bias effect, which is associated with phase coexistence of the ferromagnetic (FM) and antiferromagnetic (AF) phases, displayed a distinctive training effect, which is probably due to a competing spin order at the boundary between the FM and AF phases. Similarly, we also observed a large exchange bias and enhanced coercivity in a phase separated Pr0.55(Ca0.65S0.35)0.45MnO3 film, which had simultaneous FM and AF transitions at ∼150 K. Our results show that the exchange bias effect can be induced even in single layer films with a magnetic phase coexistence state of FM and AF phases, which may be exploited as a very simple structure for spin-valve devices.

Magneto- and electro-resistance effects in phase separated Pr0.55(Ca0.65S0.35)0.45MnO3 films

Pr0.55(Ca0.65S0.35)0.45MnO3 films were deposited on (001) (La0.18Sr0.82)(Al0.59Ta0.41)O3 substrates using pulse laser deposition technique and annealed in oxygen environment at temperatures ranging from 900 to 1100 °C, respectively. X-ray diffraction data suggested that these epitaxial films show a little relaxation in lattice strain without structural change after post-annealing within this temperature range. The as-deposited film and the film annealed at 900 °C showed only insulating and weak magnetic behaviors, but the film annealed at 950 °C depicted a clear metal-insulator (M-I) transition with a strong ferromagnetic property while increased annealing temperature lead to a slight degradation in both electric and magnetic properties. Interestingly, the slightly degraded films above 950 °C showed larger magnetoresistance and electroresistance than the optimized film at 950 °C. The temperature dependence of resistance for the film annealed at 1000 °C was measured at various magnitudes of dc current, and its peak resistance was found to decrease exponentially with increasing current. From a comparison between magnetoresistance and electroresistance, we found that the resistance was suppressed equally by either the application of a 0.7 T magnetic field or a 6 mA current.

Current effects in electronically phase-separated Pr0.7Pb0.3MnO3 single crystals

In electronically phase-separated Pr0.7Pb0.3MnO3 single crystals, current effects have been investigated systematically by combining voltage-current and specific-heat measurements. Below the metal-insulator transition temperature, the resistance increased with current at first, then decreased when the current was above a threshold value. The critical current deceased with increasing temperature and could be modulated dramatically by applying a magnetic field. By combining heat measurements, we found that Joule heat effects seem not able to be completely responsible for the nonlinear current effects. Self-optimized conducting channels or phase separation induced by the current were proposed to be other possible underlying physical processes.